Modeling of Inherent Losses of Fully Integrated Switched Capacitor DC–DC Converters

This paper presents an accurate new model for the losses related with charge/discharge process in switched capacitor (SC) DC–DC converters, named from now on inherent losses, considering especially the full integration of the converter. The model was developed for a voltage doubler and it is based on the differential equations of the circuit. It is considered that the output capacitor (C _OUT) has dimensions comparable to the flying capacitors (C _FLY). That leads to a more complex, but also more realistic, model of the circuit, especially for fully integrated converters. Usually, in SC DC–DC converters with external capacitors, C _OUT C _FLY, and a simple RC first order model can be used, but for fully integrated SC DC–DC converters, other techniques are applied to lower the voltage ripple instead of just using a large C _OUT. Simulations of a voltage doubler were performed to be used as reference and to validate the model that is also compared with other models from recent publications. The results showed that this model is more accurate in calculating the power losses of the voltage doubler across a wide range of C _FLY and C _OUT values, being a model with small complexity. Compared to simulation results, the proposed model presents a maximum relative error around 0.13%, while previous models present maximum errors that are, at least, 6%. This modeling is particularly important because it may be used in the optimization of the SC DC–DC converter taking into account the specifications and area limit, if the dynamic losses associated to the parasitic capacitances in the circuit are considered.